1. Field of the Invention
This invention relates to a microscope and, more particularly, to a microscope for observing a specimen, immersed in a liquid within a container, through the liquid and the container.
2. Description of Related Art
When a specimen, which is immersed in a liquid having a certain depth, is observed through a microscope, the thickness of the liquid layer located between the objective lens and the specimen varies depending on the position or degree of depth at which the specimen is located in the liquid. Simply using an ordinary objective lens is insufficient to obtain a satisfactory image of the specimen at any position in the liquid because the spherical aberration of the objective lens changes over a wide range according to the position of the specimen. Consequently, a specimen in a liquid is conventionally observed by one of two methods. The first of these methods involves using an objective lens having a function for correcting a spherical aberration according to the thickness of the liquid layer existing between the specimen and the objective lens. The second method involves filling the space between the objective lens and the container or the cover slip for the specimen with a small amount of liquid that has the same refractive index as the immersion liquid, and maintaining the liquid in position through the surface tension of the liquid itself.
A focusing operation and a manipulation of the aberration correcting mechanism must follow movement of the specimen in the first method. Accordingly, the overall operation of the microscope becomes complicated and troublesome. It is also difficult to stably obtain a satisfactory image.
The second method is limited to use in situations in which the working distance of the objective lens is short. If the working distance of the objective lens is long, then the surface tension of the liquid between the objective lens and the container can not be maintained.
When such a conventional microscope is used in a "weightless" or "gravity-free" environment, the drawbacks mentioned above are still present.